or Iténez
River, west-central South America.
Rising in southwestern Brazil (where it is known as the Iténez), it flows northwest past Mato Grosso city. It continues northwest, forming the border between Bolivia and Brazil, and empties into the Mamoré River above the town of Guajará-Mirim, Braz. It is navigable along its entire 1,087-mi (1,749-km) course. In contrast with the brown, silt-laden Mamoré, the Guaporé has unusually clear water; for several miles below their juncture, the two colours remain distinct.